The invention relates to a drive assembly, for motor vehicles in particular, as specified in the preamble of claim 1, and also to a process for operating a motor vehicle with such a drive assembly.
A generic drive assembly is disclosed in DE 29 43 532 A1; it has an internal combustion engine as first drive source, an electric motor, as second drive source, and a belt contact transmission as infinitely variable transmission. In the process of operation the internal combustion engine activates, by way of a coupling, the first converter element and respectively the drive wheel pair of the, belt contact transmission, while the driven wheel pair driven by way of belt contact means is connected to the driven shaft as second converter element. The electric motor is also connected directly to the drive wheel pair for the purpose of propulsion. With this drive assembly, for example, the vehicle may be set in motion and driven in the low-speed range by the electric motor by utilizing the transmission spread. If the coupling is closed on the internal combustion engine side, the internal combustion engine may be additionally engaged, and if desired the electric motor may be converted to operation as a generator. The transmission spread may also be suitably passed through by way of the internal combustion engine.
The object of this invention is to develop the generic drive assembly at low additional cost and so as to be much more versatile and favorable with respect to the transmission spread.
It is claimed for the invention that this object is obtained with the characteristic features presented in claim 1. Advantageous developments of the invention are to be found in the additional claims. In addition, claims 8 to 12 propose an advantageous process for operation of a motor vehicle with the drive assembly claimed for the invention, whereby favorable drive shaft efficiency can be achieved and emission of noxious exhaust gases may be reduced in local traffic areas, and accordingly in urban traffic.
Application of the measures claimed for the invention as presented in claim 1 yields the special advantage that the infinitely variable speed-change gear (e.g., a toroidal or belt-contact transmission) is passed through when the force flow from the first or second drive force hereafter referred to as internal combustion engine and electric motor, is reversed, the following functions being possible by means of simple switching of couplings:
1. Propulsion by way of the electric motor only for starting both forward and reverse driving in urban areas;
2. Propulsion by way of the internal combustion engine only, at higher speeds only, but if desired also for starting (emergency operation);
3. Propulsion by way of both drive sources in extreme acceleration;
4. Starting of the internal combustion engine by means of the electric motor;
5. Engagement of the electric motor as generator to supply the electric network of the motor vehicle during internal combustion engine operation and if desired in braking of the motor vehicle; and
6. Propulsion of the motor vehicle by the internal combustion engine or the electric motor without infinitely variable transmission (emergency operation).
It is also particularly advantageous if propulsive connections, such as gears, chains, etc., are provided which differ with respect to their transmission ratios. In this instance the connection switching on the electric motor, preferably a first set of spur pinions, may be designed for a higher starting torque and a lower speed range, while the connection switching on the internal combustion engine to effect propulsion, and accordingly the pertinent gear set, may be optimally designed for high speeds of the motor vehicle up to fuel-conserving overdrive operation. This propulsive connection is regularly superimposed in each instance on the spread of the infinitely variable transmission.
Smooth switching of the drive sources accompanied by low clutch wear is also achieved if reversal of the force flow is effected in the infinitely variable transmission when the speed of the elements to be coupled is synchronous. Such synchronous speed is present as a function of the given transmission ratios for the propulsive connections with a specific transmission ratio assigned to the infinitely variable transmission and can be determined more or less precisely, for example, by means of engine speed sensors on the drive shafts.
The switchable couplings may be positive claw clutches, synchronized clutches, and/or friction clutches, mounted as determined by structural relationships on the driven shaft and/or the other two transmission shafts. In the force flow on the side of the internal combustion engine in particular a clutch (single-plate dry clutch or multiplate clutch) which may also be used as starting clutch should be provided in order to make driving of the motor vehicle by the internal combustion engine possible at least in emergency operation.
Claim 8 and following claims propose operation as follows of the drive assembly described:
When the gas pedal is depressed, first the electric motor is activated by an electronic control unit with an assigned performance-value transmitter as a function of speed and/or performance and the starting torque and speed are controlled by appropriate current control. Starting at a specific speed or higher required performance (full gas or kick-down actuation if desired), the internal combustion engine is connected and activated (ignited) and its performance set at a high value, if desired with simultaneous switching from electric motor operation to internal combustion engine operation (switching of the connectable propulsive connections accompanied by reversal of force flow in the infinitely variable transmission. In the process the electric motor may feed in additional power to advantage, or again, if performance required is lower, the electric motor may be switched to generator operation to supply the electric network of the motor vehicle.
By preference the different transmission ratios of the propulsive connections are designed so that in traffic areas where speed is restricted to 30 km/hr, for example, as a rule only the electric motor is used in such areas. As a result, stages of operation of the internal combustion engine partial load ranges unfavorable to efficiency and generation of noise and exhaust gas pollution are prevented to the greatest possible extent.